PointInSetQuery silently misses most matches on selectively indexed points (fewer index dimensions than data dimensions)

Finding LFV-006Area: util / BKD pointsPriority: mediumImpact: silent wrong resultsNovelty: new

AI-assisted finding, confirmed by automated checks, not yet triaged by a human Lucene committer. This site files nothing upstream.

What it shows

You index a point field with more data dimensions than index dimensions (FieldType.setDimensions(d, 1, bytes), selective indexing) and run a PointInSetQuery (newSetQuery) on it. You expect every document whose indexed value is in the set to match. Instead BKDWriter sorts leaves by a data dimension and the query's forward-only visitor skips matches: 189,088 of 207,884 expected hits (91%) were missed in the repro, and a 3-dim/2-index-dim field returned 0 hits instead of 2.

The test shows that IntPoint.newSetQuery("f", 10, 30) misses a match on a points field with 2 dimensions of which only the first is indexed (FieldType.setDimensions(2, 1, 4)), 3 docs (30,5) (10,9) (20,9) in one segment (TestPointInSetQuerySelectiveIndexing#testSetQueryOnOneIndexDimensionOfTwo).

Expected vs actual

Expected count 2 (indexed values 30 and 10); actual expected:<2> but was:<1>: the leaf is sorted by the non-indexed dimension, so the forward-only MergePointVisitor skips 10. Fails the same way with -ea and -da, and no exception is thrown.

Files

src/org/apache/lucene/search/TestPointInSetQuerySelectiveIndexing.java (JUnit test)

Run it

Tested on Lucene main e1faeba08bde (2026-11-02): still reproduces.
Tested on Lucene main 645d4fe14a20 (2026-10-28): reproduced.
Recorded outcome of run 1 on Lucene main 645d4fe14a20: 1 test(s) run, 1 failed.
How to read the outcome: a failing test is the finding reproducing (the failure message states expected against actual).
Seeds: a rerun with the same seed replays the same random choices. Assertions off (-da -dsa -Dtests.asserts=false) is the production-like setting.

# Lucene checkout at the tested commit, built with: ./gradlew --no-daemon assemble   (JDK 25)
LUCENE=/path/to/lucene; V=12.0.0-SNAPSHOT
CP=$LUCENE/lucene/core/build/libs/lucene-core-$V.jar
CP=$CP:$LUCENE/lucene/codecs/build/libs/lucene-codecs-$V.jar
CP=$CP:$LUCENE/lucene/test-framework/build/libs/lucene-test-framework-$V.jar
CP=$CP:randomizedtesting-runner-2.9.2.jar:junit-4.13.2.jar:hamcrest-3.0.jar   # test-framework dependencies (Maven Central)
CP=$CP:junit-platform-console-standalone-6.1.3.jar   # JUnit Platform console launcher (Maven Central)

javac -d classes -cp "$CP" $(find src -name '*.java')

# run 1: assertions on, seed DEADBEEF
java -ea -esa --add-modules jdk.incubator.vector --enable-native-access=ALL-UNNAMED -Dtests.seed=DEADBEEF \
     -cp "classes:$CP" org.junit.platform.console.ConsoleLauncher \
     execute --select-class org.apache.lucene.search.TestPointInSetQuerySelectiveIndexing

Gradle alternative: copy the test into the matching module's src/test/ tree of the checkout and run ./gradlew -p lucene/<module> test --tests <class> -Ptests.seed=<seed> (add -Ptests.asserts=false for a run without assertions).

Formal models and scripts this finding's part of the hunt used: study-bkd-points-proof

Feedback

Open an issue in lucene-ai-bug-hunt. Please do not open issues or pull requests in apache/lucene about this finding unless a Lucene committer agrees it should be filed.

Snapshot of 2026-11-04. AI-assisted; not yet triaged by a human Lucene committer. Feedback: open an issue in lucene-ai-bug-hunt.